New to geared bikes and feeling slightly overwhelmed

Hello friends,

after only ever riding single speed bikes, I want to build my first geared bike and I need some guidance. If any of you have the time to point me in the right direction, that'd be very much appreciated.

I got this here frame recently. My plan was to do some light gravel/touring with it, with a 1x chainring because I don't need the bulk of a front dereilleur.

I figured buying a drivetrain would be a 5 minute affair because it's cranks, a ring, a cassette, dereilleur and shifter, and it must all be compatible standards, right?

Well, looking for components made me realize that despite loving cycling so much, I know nothing about it. I'm being asked to decide "bolt circle mount options" between 1 – 12-fold compatibility (?), offset amount, which sprocket mount and gradation and whether my shifters will be Shimano or Microshift or….

I would really love to pull this off myself instead of giving up and getting a bike shop to do this. I want to learn more. If someone could give me helpful suggestions about what goes together, I can go from there and look up further guides myself.

Thanks a bunch!

Notes:

• I want my components to be silver, not black
• Ideal budget would be 200-500£
• I want to use riser bars, not drops, so shifting would need to be compatible with levers that mount on flat bars